class Student(object):
    count = 0

    def __init__(self, stuname):
        self.stuname = stuname
        Student.count += 1
        
if Student.count != 0:
    print('失败!')
else:
    ben = Student('yes')
    if Student.count != 1:
        print('失败!')
    else:
        lana = Student('yes')
        if Student.count != 2:
            print('失败!')
        else:
            jack = Student('yes')
            if Student.count != 3:
                print('失败!')
            else:
                print('Students:', Student.count)
                print('通过!')